Filter cartridge with reuseable framework

ABSTRACT

A filter cartridge comprising a framework and a surrounding envelope of filter material. The framework is reusable and provided with a rough, granular surface texture to provide increase surface area available for the propagation of aerobic bacteria. The envelope is disposable. Thus, biological filtration of the water provided by the aerobic bacteria is not interrupted upon replacement of the filter material. A second filter medium may be disposed within the envelope. The envelope is held in place by a pair of flaps which sandwich an edge of the filter material.

BACKGROUND OF THE INVENTION

The invention relates to the field of filters and in particular to thefield of aquarium filters and filtering equipment.

In the art of home aquariums, it is known to use a filter system whichcontinuously circulates the water through a filter medium and returns itto the aquarium. One type of aquarium filter system is of the externaltype and uses a small container mounted on the side of the aquariumwhich holds the filter medium. The water from the aquarium is drawnthrough filter material in the container by means of a water pump andthen returned to the aquarium. The filter medium is usually in the formof particles of activated carbon or charcoal and a fluffy mass ofsynthetic resin fibers.

An external tyoe of filter is shown in U.S. Pat. Nos. 3,513,978 toNewsteder and 3,525,435 to Conner.

The Newsteder device uses two separate compartments, each filled with adifferent filtering substance (i.e, fibrous filtering material andcharcoal). The water flows through the fibrous material to the charcoal,through the charcoal and is then returned to the aquarium. In this typeof filter, however, the compartment holding the charcoal must have veryrestricted openings to prevent the flow from washing away any charcoaldust or particles into the aquarium.

The Conner filter uses a perforated top with a depending filter bag thatis filled with charcoal. The flow of the water is down through the top,out through the bag walls and returns to the tank. The Conner filter iswholly disposable. However, it allows waste particles to contaminate thecharcoal as there is no filtration prior to its passage through thecharcoal.

Another type of aquarium filter is the internal or underwater filter. Acontainer is provided which includes a filter medium such as activatedcarbon or charcoal and a fluffy mass of synthetic resin fibers. An airlift is provided extending from the container and air is pumped downinto the air lift from an external air pump. The air pumped into the airtube flows up through the air lift causing a suction to draw water intothe container, pass it through the filter medium and up through the airlift along with the air bubbles.

In aquarium filtration, the filter medium provides various types offiltration activity. As the water flows through a porous wall,mechanical filtration of the water occurs with the walls acting as asieve, retaining the solid contaminants. The activated carbon orcharcoal provides a chemical filtration of the contaminated water. Atthe same time bacteria in the form of accumulated sludge and slime actupon the waste material dissolved in the water, thus providingbiological filtration.

The most effective water purification is achieved when bacterialpropagation is at a high point. However, at this point prior art filtercartridges usually become subject to clogging and must therefore beremoved and replaced. The newly replaced filter cartridge is free ofbacteria while the old filter cartridge with bacteria is discarded.

Because the entire filter cartridge is discarded, the filter itselfloses the biological filtering effects of micro-organisms. Theseorganisms are natural filters because their life functions convert manyof the harmful toxic wastes into harmless nitrates. In existing filtercartridges the entire cartridge is sealed and is completely replacedwhen it becomes clogged. Any bacterial organisms which may have grownwithin the filter cartridge are therefore discarded with the cartridgeitself. This creates a void in filtering ability until the organismsre-establish themselves in the replaced filter cartridge. Additionally,since the filter cartridge is entirely sealed, the amount of carbonparticles or other type of filtering material in the cartridge cannot beindividually adjusted by the aquarium user himself.

SUMMARY OF THE INVENTION

The filter cartridge of the invention provides a reusable frame which isinserted inside a disposable filter bag or envelope that can be filledwith filtration material. The framework is conducive to settlement,growth and propagation growth of micro-organisms. The reuse of theframework without destroying the bacteria provides the filter systemwith uninterrupted biological filtering action.

The frame is constructed with laterally projecting separators. Theseparators extend across the filter cartridge. They have a narrowdimension transverse to the flow of the aquarium water thereacross so asto cause only minor constriction of the flow. The separators have abroad dimension parallel to the direction of flow, and serve to spaceapart the walls of the filter bag in which the frame is contained. Thesurface of the frame is textued to provide increased available surfacearea, supporting the growth of organisms active in biologicalfiltration.

The filter cartridge further provides an internal structure for thefilter bag or envelope. In this way the water may be circulated throughthe filtration material from one side of the envelope, through theinterior space of the envelope and out the second side. The first wallof the filter envelope filters out large contaminants before reachingthe filtration material, such as carbon, which is disposed within theenvelope. This prevents clogging and, therefore, early failure of thecarbon. The second wall of the envelope prevents carbon dust, which maybe picked up by the flow, from being carried out of the filter into theaquarium.

The wall of the filter envelope is comprised of a water permeable filtermembrane structure. The membrane is formed of an open web of closelyspaced or randomly disposed fibrous or filamentary material which formsa matrix and provides numerous interstices or pores defining waterpassages. Passage of the water through the interstices in the membranestructure causes mechanical filtration of the water by retaining thesolid waste and contaminants.

The roughened, textured, or etched surface of the framework provides amatte finish which increases surface area for the growth of organismsactive in biological filtration. This, in combination with the presenceof oxygenated water, provides an environment conducive to bacterialpropagation. Such aerobic bacteria which propagate cause purification ofthe contaminated water by acting upon, digesting or converting the toxicmaterials accumulating in the filler and those dissolved in the waterinto products which are harmless to aquatic life in the aquarium.

The filter cartridge can be inserted in an external or an internalfilter such as a corner or bottom filter. The soft filter envelopecovering the rigid or semi-rigid frame creates a better seal along itsedges when slid into position in the filter box itself. This eliminatesthe need for perfect measurements for the sealing area and also preventsbreaking or scratching the wall of the filter box.

Additionally, the filter cartridge can be used as a filtering device byitself by causing a flow of the aquarium water through the filtercartridge.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an external filter using the filtercartridge of the invention;

FIG. 2 is a partially broken away front elevational view of the filtercartridge of the invention with the frame partially removed;

FIG. 3 is an exploded perspective view of the filter cartridge;

FIG. 4 is a vertical, cross-sectional view of the filter cartridge;

FIG. 5 is a horizontal, cross-sectional view of the filter cartridge;

FIG. 6 is an enlarged microview of the textured surface of the frame;

FIG. 7 is a cross-sectional view taken along line 7--7 of FIG. 6;

FIG. 8 is a perspective view of a frame, in accordance with anotherembodiment of the present invention;

FIG. 9 is a front elevational view of yet another embodiment of theframe;

FIG. 10 is an enlarged cross-sectional view of the upper end of thecartridge showing a closure mechanism;

FIG. 11 is a side elevational view of the filter bag showing a method offorming the bag;

FIG. 12 is a cross-sectional view taken along line 12--12 of FIG. 11;

FIG. 13 is a perspective view of an internal, underwater filter assemblyusing the filter cartridge of the invention;

FIG. 14 is a side sectional view showing the use of the filter assemblyof FIG. 13 inside the aquarium tank;

FIG. 15 is a top schematic view showing the use of the filter cartridgeitself as a filtering device;

FIG. 16 is a view taken along lines 16--16 of FIG. 15.

In the various figures of the drawing, like reference charactersdesignate like parts.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 2, 3 and 4, there is shown the filter cartridge 1 ofthe invention. The cartridge includes the frame 2 and a filter envelope3. Charcoal or other filtration material 13 can be placed into theenvelope.

Filter envelope 3 is formed of any suitable filter material and may beconstructed of synthetic resin fibers in a random or non-woven pattern.The envelope has a front wall and back wall which are joined on three ofthe four perimeter edges of each.

The frame 2 can be molded plastic. It includes a perimeter defining aframe formed by top portion 4, bottom portion 5 and side portions 6. Twoflaps 7 are hingeably attached to the top edge of top portion 4. In thepreferred embodiment the flaps 7 are integrally molded with the frameand provided with plastic living hinges 8, that is portions of plasticwhich are flexible and resist fatigue failure. However, the flaps may beattached in any known manner.

Traversing the interior of the peripheral frame are a plurality ofseparators 9. The separators extend laterally beyond the front and backof the frame surface in the direction of flow of the water beingfiltered when the cartridge is in use. In FIGS. 2-5, the separators areshown as vertical flanges which have a narrow thickness in the directionparallel to the top portion 4 and bottom portion 5. This minimizes thesurface area which is transverse to the flow of the water being filteredwhen the cartridge is in use. The separators 9 have a width which isone-half to three-quarters of an inch for an envelope which is aboutfour inches by six inches. The width is measured in a directionperpendicular to the plane of the perimeter defining frame; that is,parallel to the direction of flow when the cartridge is in use. Thereare similar flanges or separators 10 extending from side portions 6 ofthe frame.

In use, the frame is positioned within the filter envelope. A secondtreatment material such as activated carbon or activated charcoal 13 maybe added to the envelope and the flaps 7 are folded down, sandwichingthe upper edge 11 of the filter envelope 3 between the flap 7 and topportion 4. When the assembled cartridge is inserted into a filterassembly, the flaps will normally be held down. However, optionally, inorder to assure that the flaps hold the envelope tightly, a clip 12 canbe used. The clip is also useful in preventing the escape of filteringmaterial in shipping the cartridge pre-assembled. The clip is U-shapedand is snapped over the flaps 7 once they have been folded down. Theclip biases the flaps toward one another thus holding the envelope. Itshould be understood that other suitable biasing means may also be used,such as molding the flaps 7 and frame so the flaps are resilientlybiased in the sandwiching position.

The separators hold the opposing front and back walls of the envelope inspaced relation. As the watr is forced through the filter, it passesfirst through the front wall, which initially filters the water. It thenpasses through and is treated by the carbon or charcoal 13 or otherfiltration material placed in the envelope. Finally, the water flowsthrough the back panel of filter material which causes secondaryfiltering and prevents the passage of charcoal particles to theaquarium. The two-wall filtering allows freer water flow, as the filterclogs in parts with waste and biological activity.

The filter cartridge can be used in connection with a filter mechanismsuch as that depicted in FIG. 1. The mechanism is an external filterassembly and has a tank 14 which receives the filter cartridge. Thefilter cartridge is slideably received in two opposing grooves 15 in theside walls partially defining a clear water chamber 16 in the front anda filtering chamber 26 in the rear. Water from the aquarium is pulledinto the filter tank through pipe 17 by a water pump 18. The pump has animpeller 19 and drive motor 20 which are magnetically coupled in anyknown manner. Pipe 17 has a strainer 21 on the intake end so as toprevent pulling in fish or other objects which may jam or damage theimpeller in the pump. The aquarium water is pulled into a receivingchamber 22 which is partially separated from filtering chamber 26 bydivider 23. Divider 23 is spaced from back wall 24 of the tank. Waterpumped into receiving chamber 22 is allowed to flow into the filterchamber 26 behind the filter cartridge. The rising water level in thefilter chamber 26 between the filter cartridge and the back wall andunder the force of gravity the water to flow through the interstices inthe material of the filter cartridge. The water passing through thefilter cartridge wall is mechanically cleaned of contaminants in asieve-like manner. Once within the filter envelope, the water is furthercleansed by the carbon within the envelope and aerobic bacteria whichgrow on the frame and surfaces of the filter envelope. The water passesthrough the second wall and is subject to secondary filtration thereby.The water passes through the envelope wall to the clear water chamber16. As the water level in this chamber rises, it reaches the level ofspillway 25 and spills back into the aquarium.

When the filter cartridge becomes clogged with contaminants, it isremoved, the envelope, the carbon and other filtration material arediscarded and a new envelope positioned on the frame. New carbon andother filtration material is placed within the envelope and thecartridge is replaced in grooves 15 and the filtering process continues.

In addition to mechanical filtration, biological filtration is by farthe most important type for removal of toxic waste within an aquarium.In biological filtration, the aquarium water is conditioned as a resultof the presence of living organisms, primarily bacteria. The presence ofthe bacteria serves to convert toxic waste into end products which arenot harmful to the aquatic life. The type of bacteria that serve toconvert the toxic waste, and especially ammonia, into nitrates which arenot harmful, are aerobic bacteria. Aerobic nitrifying bacteria have twobasic requirements in order to propagate: high oxygen concentrations anda place to attach themselves. The oxygen is generally provided withinthe aquarium tank by means of a natural interchange at the surface ofthe water. The water flowing back into the aquarium from the filter isaerated and brings a fresh supply of oxygen to the aquarium water.

The bacteria adhere in some degree to almost any surface available tothem. Such surfaces will naturally include the filter cartridge,especially the frame contained within the cartridge. The frame isespecially suited for the growth of bacteria because it is in the pathof the constant flow of water laden with dissolved contaminants. Suchcontaminants include toxic ammonia which serves as the nutrient for thegrowth of the bacteria. Accordingly, the frame serves as an excellentlocation for the propagation of organisms which cause biologicalfiltration of the aquarium water.

The propagation of such bacteria increases with time. In fact, a commonmethod of starting biological filtration is to begin with some gravel orsome filter material from an established aquarium on which the bacteriahave already propagated. Placing such substances having bacteria on itinto the aquarium permits the bacteria to propagate as they feed on thewaste products in the aquarium.

With prior art filter cartridges, when the cartridge became clogged withcontaminants, the entire cartridge was removed. Therefore, any build upof microorganisms useful in biological filtration was thrown away.Insertion of a new, clean filter cartridge which would not have anybacteria present, therefore, would recuire that the biologic filtrationprocess begin anew on the replaced filter cartridge.

In the present invention, the reuseable frame insures the presence ofthe microorganisms needed for biological filtration. Any build up ofsuch bacteria is retained on the frame itself. The frame can be cleanedin cold water which does not destroy the organisms. Placing the frameinto a new envelope retains the organisms previously propagated andpermits continued enhancement of the biological filtration processrather than a restarting of the process.

Since a large surface area provides many more aerobic nitrifyingbacteria with a place for attachment the surface of the framework can beetched, sandblasted, or the like, to provide a rough, granular surfacetexture typically referred to as a matte finish. FIG. 6, shows anenlarged section of the framework 27 which includes the granular surfacetexture 28. As shown in FIG. 7, the surface includes protrusions 29 andvalleys 30 along the surface of the frame. Such protrusions and valleysdefining the roughened texture substantially increase the surface areabeyond that normally required for structural purposes. However, thebacterial organisms use the protrusions and valleys as adhesion areas onwhich they can propagate. In this manner, the amount of surfaceavailable for the propagation of the organisms is dramatically increasedto permit enhancement of the biological filtration provided by thefilter.

The frame can be formed by a sandblasting operation in conjunction witha molding process. Either the mold itself can be initially sandblastedin which case each time the frame is molded it will be produced with arough granular surface. Alternately, a smooth mold can be utilized andthe end product frame resulting from the mold can be sandblasted toproduce the granular texture on the surface. Another approach would beto etch the rough surface using a chromic acid, or other type of etchmaterial.

The reusable frame assembly provides additional benefits. Existentdisposable filter cartridges are completely sealed. They include theexterior envelope which contains charcoal or other filter material. Theuser never has an opportunity to verify the type of carbon or charcoalutilized or any other type of filtration material that may be in theenvelope, and is never certain of the quality or amount of such materialpresent in the filter. With the present invention the user can open theenvelope, and verify the presence and type of the activated carbonutilized. In fact, the user can add additional carbon or other waterconditioning materials and can select the type that he desires to use.In this way, the filter cartridge can be tailored by the user to theindividual needs and requirements of his aquarium. The carbon can alsobe removed, which is useful in tanks where diseased fish are beingtreated with medication and where chemical filtration must be stoppedwhile continuing the mechanical and biological filtration.

It should also be appreciated that the present structure provides thatthe frame is internally of and slidable with respect to the envelope.There is no permanent attachment between the frame and the filterenvelope. As a result, there is no wasted portion of the envelope whichmight be required for attachment to a frame. This allows the envelope tobe filled with more material.

The separators traversing the perimeter of the frame need not be onlyvertical flanges or blades. Other configurations can also be utilized.By way of example, FIG. 8 shows a peripheral frame 31 having a top andbottom wall 32, 33 and opposing side walls 34, 35. Flaps 36, 37 arehingedly connected at the top 32 to close onto the envelope. Threehorizontal shelves or trays 38a, 38b, 38c serve as the separators. Thetrays extend laterally beyond the front and back surface of the frame toprovide adequate spacing of the walls of the envelope when the frame isinserted within the envelope.

Using the horizontal trays 38a, 38b, and 38c, there is provided theadditional benefit that any charcoal or activated carbon inserted withinthe envelope will be retained by the trays and will spread the charcoalto various levels within the filter envelope. This will avoid thetendency of the charcoal to settle at the bottom and will insteadprovide a distribution of the charcoal throughout the height of thefilter cartridge.

FIG. 9 shows yet a further arrangement wherein the frame 40 includes aseparator arrangement having an inner circle 41 surrounded by aconcentric outer circle 42 and connected by a plurality of webs 43 inthe form of spokes. The outer circle 42 is spaced from the periphery bymeans of additional webs 44 also in the form of spokes. With thearrangements shown in FIG. 9 the charcoal will be retained by the spokesand provide a distribution throughout the interior of the envelope.

In all cases, the separators are thin so as not to impede the flow ofwater through the filter envelope. They also extend laterally forwardand behind the frame surface to adequately space apart the walls of thefilter envelope.

In order to retain closure of the flaps onto the envelope, as shown onFIG. 10, the upper wall 32 of the frame can include a plurality oflaterally extending dimples 45. A corresponding plurality of receivingapertures 46 are provided each of the side flaps 36, 37. As the sidewalls of the envelope 48 are placed between the flaps and the frame, theprojecting dimples 45 penetrate into the woven material of the envelopeto extend there through. Closure of the flaps onto the dimples permitthe apertures 46 to engage the dimples thereby securing the envelope inplace. This prevents the envelope from sliding down off the frame workeven if it becomes heavy as a result of the weight of the water as wellas the presence of the charcoal and any sludge and contaminants that maybe retained within the envelope.

Preferably the envelope is made of non-woven reticular filter material.As shown in FIGS. 11 & 12, a sheet of such non-woven mat filter material50 can be formed into a cylinder by wrapping it about its longitudinalaxis and stitching the two joining longitudinal ends 52 & 54 togetherwith stitches 56. The edge portions 58 & 60 beyond the stitching 60 meshtogether to close the gap formed by the stitches. The meshed portion canthan be pressed onto the cylinder 50 so that it overlies the stitchedpart 56. This gives a doubled over portion at the stitching 56 so thereis no loss of thickness at that location. The envelope can then becompleted by squeezing the back of the cylinder 50 together andstitching 64 along the bare edge thus formed. In this way the filterenvelope can be formed of a single sheet of non-woven material.

As is noted in FIG. 1, the external filter assembly is preferably formedof molded plastic material. In order to extract the molded housing fromthe mold using an injection molding process, it is noted that the shapeof the assembly is downwardly tapered. In a similar manner, thecorresponding shape of the frame as shown in FIGS. 3, 8, 9, and othersis likewise downwardly tapered to fit into the sideward grooves providedin the filter assembly.

As best noted in FIG. 3, the envelope 3 need not be made with acorresponding tapered shape. The width of the envelope can be made of asize approximately corresponding to the narrow tapered end of the frame.Because of the construction of the bag of non-woven reticulatedmaterial, the bag stretches as the frame enters inside the bag. Thismakes the bag fit tightly onto the frame and causes the bag to grip theframe and provide a snug fit. At the same time, it is not too tight sothat it can still be removed for replacement when needed.

As is noted in the drawings, the lateral side edges of the filtercartridge have the envelope as the exterior edge. Since the envelope isformed of a non-woven soft material, as the filter cartridge is insertedinto the grooves 15 provided on the side of the filter assembly shown inFIG. 1, the envelope grips the rails within the grooves and gives atight fit of the filter cartridge within the filter assembly. Thisprevents leakage of the contaminated water around the sides of the bagand prevents flow of the contaminated water into the clean waterchamber.

The filter cartridge of the present assembly was shown in FIG. 1 for usein an exterior filter assembly which uses a water pump. The cartridge,however, can also be utilized in numerous other types of filterassemblies of various configurations, including the internal orunderwater filter, as shown in FIGS. 13-14. By way of example, there isshown an underwater or internal filter 70 including a substantiallyrectangular tank or housing 72. The housing 72 includes a front wall 74having a plurality of holes or perforations 76 to permit entry of thewater. A pair of side rails or U-shaped channels or grooves 78 andpositioned laterally on either side of the housing. The filter cartridge80 of a type heretofore described in connection with the invention canbe slid into the side rails so as to separate a front chamber 82 from arear chamber 84. The front chamber receives the contaminated water whichthen passes through the filter cartridge of the invention and thenenters into the rear or clear water chamber 84 behind the filtercartridge. A removable cover 86 is provided on the housing 72 to sealthe top of the cartridge and permit entry into the housing or tank 72for removal of the filter cartridge.

Rearward of the housing 72 is formed an air lift tube 88 which can beintegral with the housing. A passageway 90 communicates between theclear water chamber 84 and the interior 92 of the air lift tube 88.

An air pipe 94 extends downward into the interior 92 of the air lifttube 88. An air pump 96 serves to pump air through the air pipe into theair lift tube. Typically, an air stone 98 may be placed at the lower endof the air pipe proximate the passageway 90 into the clear waterchamber.

During operation, air pumped through the air pipe exits through the airstone at the lower end of the air pipe and travels upwardly through theair lift tube 88. The flow of air upwardly causes a suction drawing theclear water from the clear water chamber 84 along with it upwardlythrough the air lift tube and back into the aquarium. This flow of theclear water from the clear water chamber 84 causes a suction whichbrings the contaminated water from the aquarium through the holes 76 inthe front wall of the housing to thereby provide a continuous flowthrough the filter assembly.

As before, it is noted that the housing is slightly downwardly taperedas a result of the injection molding process. Again, the correspondinglyshaped taper of the filter cartridge will fit into the housing assemblyand the presence of the soft envelope will provide a tight fit into theside grooves 78 in the housing assembly.

Although the use of the filter cartridge has been shown in connectionwith external filters utilizing water pumps as well as internal filtersusing air pumps, it will be shown in FIGS. 15 and 16 that the filtercartridge itself can provide an entire filter assembly without an entirefilter unit. As shown, the filter cartridge 100 of the present inventionis placed vertically across a corner in the aquarium 102 extendingdiagonally between the corner walls 104 and 106. In order to hold thefilter cartridge in place, side suction cups 108, 110 can be connected.Other attachment or securement means could be utilized. In addition, thecartridge could simply be stuck into the gravel 112 provided at thebottom of the aquarium 114. It should be appreciated, that as the filtercartridge gets further clogged it actually sticks tighter and remainsmore securely in place.

An air tube 116 extends down behind the filter cartridge 100 and an airstone 118 may conveniently be placed at the distal end of the air tube116. Through the use of an external air pump, air would be pumpedthrough the pipe 116 resulting in a flow of air bubbles 120 from thelower end of the tube or the air stone 118 if it is utilized. The upwardflow of bubbles 120 causes a suction behind the filter cartridge 100 tocause the water to flow into the front of the cartridge as shown by thearrows 122. Thus the cartridge by itself can serve as a filter byinserting it into the aquarium and causing a suction behind one wallcausing a flow path of the aquarium water through the filter cartridge.

Thus, it is seen that by providing a reusable internal support frame,the filter of the invention continues to increase the biologicalfiltration in the aquarium. The envelope-frame combination also providesan easy maintenance filter with disposable filter material.

I claim:
 1. A water purifying cartridge assembly for use with afiltering mechanism for an aquarium of the type which mechanicallyfilters the water by passing it through the filter cartridge,comprising:(a) an envelope of filter material having at least two sidewalls interconnected along three edges thereby defining an inner space,a fourth edges being open to define a mouth into the inner space; (b) asubstantially rigid framework extending along the envelope removablyinsertable through said mouth into said inner space to support saidenvelope; and (c) means for separating the walls of the envelope toposition said walls in spaced relation.
 2. The water purifying cartridgeaccording to claim 1, further comprising a second purifying materialdisposed within said envelope.
 3. The water purifying cartridgeaccording to claim 1, wherein said means for separating the walls of theenvelope are flanges provided on said framework to position said wallsin spaced relation.
 4. The water purifying cartridge according to claim3, wherein said flanges are members laterally projecting forwardly andrearwardly of said framework in the direction of flow of water throughthe filter cartridge, and being narrow in the direction perpendicular tosuch flow, said flanges traversing the interior of the supportstructure.
 5. A water purifying cartridge assembly as in claim 1, andfurther comprising a rough, granular surface texture on said frameworkwhich increases the available surface area of the framework for thepropagation of organisms which participate in biological filtration ofthe water.
 6. A filter cartridge for use with an aquarium, of the typeplaced in the flow path of a continuously recirculating system of waterform the aquarium comprising:(a) a framework; (b) a disposable enveloopeof filter material having a pair of opposing walls interconnected alongthree edges to define an inner space, a fourth edge being open to definea mouth into the inner space through which said framework is removablyinsertable and whereby said opposing walls of said envelope aremaintained in spaced relation; and (c) retaining means to detachablyretain said fourth edge such that the envelope is in surroundingrelation on said framework.
 7. The filter cartridge according to claim1, wherein the framework has a rough, granular surface texture toincrease the availble surface area for supporting the propagation oforganisms active in the biological filtration of aquarium water.
 8. Thefilter cartridge according to claim 6, further including flangesextending from said framework to maintain the opposite inward facingwalls of said envelope in spaced relation.
 9. The filter cartridgeaccording to claim 8 wherein said flanges traverse the interior of theframework and define members laterally projecting beyond the front andrear of the framework in the direction of flow of the water, and havinga narrow dimension in the direction perpendicular to the flow of thewater.
 10. The filter cartridge according to claim 9, wherein saidflanges extent horizontally across the framework to permit retention ofadditional purifying granules disposed within said envelope.
 11. Thefilter cartridge according to claim 6, whereas said framework has itswidth downwardly tapered, and whereas the width of the envelopeproximates the narrow end of the framework whereby the envelope isstretched to receive the framework to provide a grip of the envelopeonto the framework.
 12. A filter cartridge for use with an aquarium, ofthe type placed in the flow path of a continuously recirculating systemof water from the aquarium comprising:(a) a framework; (b) a disposableenvelope of filter material defining an inner space into which saidframework is removably disposed and whereby opposite inward facingsurfaces of said envelope are maintained in spaced relation; and (c)retaining means to detachably retain said envelope of filter material insurrounding relation on said framework, wherein: (d) said envelopeincludes an opening along an edge thereof, through which said frameworkis disposed within said envelope; and (e) said retaining means includesa pair of flaps disposed on a cross member of said framework positionednear the opening of said envelope for closing onto the envelope tosandwich a portion of said envelope between said flap and said crossmember.
 13. The filter cartridge according to claim 12, and furthercomprising means for biasing the flaps to close onto the envelope.
 14. Afilter cartridge for use with an aquarium, of the type placed in theflow path of a continuously recirculating system of water from theaquarium comprising:(a) a framework; (b) a disposable envelope of filtermaterial defining an inner space into which said framework is removablydisposed and whereby opposite inward facing surfaces of said envelopeare maintained in spaced relation; and (c) retaining means to detachablyretain said envelope of filter material in surrounding relation on saidframework, wherein said envelope comprises a single sheet of materialwrapped around into a cylindrical configuration, opposing longitudinalends stitched together, said ends being pressed down onto the cylinderagainst the stitching to provide an overlying layer onto the stitchedtogether portion to retain the thickness of the material at the stitchedportion.
 15. The filter cartridge according to claim 14, wherein theopposing edges of the sheet beyond the stitching mesh together to form asubstantially continuous cover over the stitching.
 16. The filtercartridge according to claim 14, and comprising stitching along the baseof the envelope to close the bottom thereof.
 17. The filter cartridgeaccording to claim 16, wherein the envelope is formed of non-wovenreticulated material.
 18. A disposable envelope for use in an aquariumfilter cartridge, comprising opposing walls of non-woven foraminousfilter material, means for interconnecting said walls along three sidesthereof and defining a mouth along a fourth side for receiving therein aframework of the filter cartridge, and an inner space between said wallsfor receiving therein filter material, wherein said envelope comprises asingle sheet of material wrapped around into a cylindricalconfiguration, opposing longitudinal ends stitched together, said endsbeing pressed down against the stitching to provide an overlying layeronto the stitched together portion to retain the thickness of thematerial at the stitched portion.
 19. The disposable envelope as inclaim 18, wherein the opposing edges of the sheet beyond the stitchingmesh together to form a substantially continuous cover over thestitching.
 20. The disposable envelope as in claim 18, and comprisingstitching along the base of the envelope to close the bottom thereof.21. The disposable envelope as in claim 18, wherein the frameworkinsertable into the envelope has downward taper, and wherein the widthof the envelope proximates the narrow end of the framework.